This invention relates to sutures and more particularly to compacted braided silk sutures of increased tensile strength and knot strength, and to methods of making the same.
In the suture art, the term "braided suture" means a substantially symmetrical strand formed by crossing a number (at least three) of individual strands, called "carriers", composed of one or more threads diagonally in such a manner that each strand passes alternatively over and under one or more of the others. The braided suture may, if desired, include a core section composed of one or more threads around which the braid is externally fabricated.
The term "uncompacted braided suture" means a braided suture which has not been subjected to any compacting force following its preparation and which is characterized by a relatively loosely braided structure.
The term "compacted braided suture" means a braided suture which has been subjected to a stretching force or other compacting force whereby the diameter of the suture has been decreased.
Uncompacted braided silk sutures of the prior art have customarily been stretched under the influence of heat to decrease the diameter of the suture by making it more compact and consequently to increase its strength per square inch. These stretched braided silk sutures offer many advantages over unstretched sutures. Stretching of the suture makes it possible to prepare the strongest suture for a given suture diameter. By compacting the braided suture and thus reducing the volume of the voids therein, it becomes possible to increase the number of threads within a given diameter. In effect, the cross-section of the compacted braided silk suture approaches that of a monofilament.
Compacted braided silk sutures have advantages over monofilament sutures, notably in their flexibility and dependability. Another advantage of compacted braided silk sutures is that the compact nature of the braid reduces capillarity, which in turn inhibits the spread of infection along the suture. The tightness of the braid also reduces an undesirable "brooming" effect, i.e., the flaring of individual threads of the braided suture when the same is cut. Further, because of the smoother surface of the compacted braided silk suture resulting from the stretching operation, less tissue trauma is likely to occur from the use thereof.
The effectiveness of any method of stretching braided sutures is limited by the percentage stretch which can be achieved without substantially damaging the threads of the suture. The greater the percentage stretch without damaging the threads, the greater the decrease in diameter of the suture and the greater the increase in tensile strength and knot strength per square inch--which criteria characterize a suture. In general, the hot-stretching technique of the prior art as applied to silk sutures is limited to a percentage stretch of about 5-10%, since silk fibers are not thermoplastic. Stretching substantially beyond 10% by the hot-stretching technique of the prior art results in substantial fiber breakage and, consequently, in a weaker, fuzzy suture. Thus, hot-stretching of silk without damage to the fibers is severely limited in the percentage stretch which can be obtained thereby.